The present invention relates to a packet switch with a switching architecture comprising a cross network of input- and output stitching links respectively crossing each other.
Below follows a survey of some practically existing or suggested architectures:
Square matrix PA1 Common medium of ring or bus type PA1 Single-path-network, e.g. Batcher-Banyan- or Delta-networks. PA1 Multi-path-networks, e.g. Clos- or Benes-networks.
As far as large switches are concerned architectures which are not of square structure are foremost discussed internationally. A packet switch with a square matrix has, however, many desired properties. It is free of congestion, it admits simple routing and manages point to multi point connections. On the other hand it is difficult to expand as the amount of hardware grows in proportion to the square. It is also difficult in large matrixes to solve the problem of multiplexing traffic from the rows to the columns of the matrix. Proposals for solving this problem mostly imply that some form of control algorithm communicates towards the buffers of the cross points and thereby distributes the bandwidth of the column between the cross points.
Up to a maximum size a switch with a common medium has the same properties as the square one. It has, however, a limited size as the common medium shall carry the sum of bandwidths connected to the switch. It is therefore not suitable for a large broadband packet switch.
A switch consisting of a single-path-network has the property that two packets can desire to reserve an internal link in the network simultaneously. As there is no buffering in the network one of the packets therefore has to be eliminated (a form of internal lock).
To prevent this there must be complicated algorithms for selection and sorting of the packets. There is so far no good and simple solution to this problem.
In some cases a multi-path-network is an extension of single-path-networks for solving the problem described above.
These networks can be dimensioned to decrease the internal congestion and, as far as CLOS-networks are concerned, also be dimensioned free of congestion. As the name indicates there are several alternative routes through the switching network to one and the same output. Thus the routing algorithm becomes considerably more complex than for the single-path-networks.
Through U.S. Pat. No. 4,876,681 a packet switch is known, which has a network configuration aiming at enabling network expansion and change of configuration.
The switch includes a number of "configuration units" connected in a hierarchical tree structure, where the number of hierarchical steps or levels can be selected according to the size of the network.
In the respective configuration units of the tree structure a fifo buffer is arranged. The packet transfers to the next step of the hierarchical tree structure are made in dependence of supervision of the state of the fifo buffer in said next step. If the fifo buffer in the next step is not empty the packet data is kept in the own internal fifo buffer.